Spectral- and size-resolved mass absorption efficiency of mineral dust aerosols in the shortwave spectrum: a simulation chamber study

This paper presents new laboratory measurements of the mass absorption efficiency (MAE) between 375 and 850 nm for 12 individual samples of mineral dust from different source areas worldwide and in two size classes: PM10:6 (mass fraction of particles of aerodynamic diameter lower than 10.6 \u3bcm) and PM2:5 (mass fraction of particles of aerodynamic diameter lower than 2.5 \u3bcm). The experiments were performed in the CESAM simulation chamber using mineral dust generated from natural parent soils and included optical and gravimetric analyses. The results show that the MAE values are lower for the PM10:6 mass fraction (range 37\u2013135x10-3 m2 g-1 at 375 nm) than for the PM2:5 (range 95\u2013711x10-3 m2 g-1 at 375 nm) and decrease with increasing wavelength as lambda-AAE, where the \uc5ngstr\uf6m absorption exponent (AAE) averages between 3.3 and 3.5, regardless of size. The size independence of AAE suggests that, for a given size distribution, the oxide fraction, which could ease the application and the validation of climate models that now start to include the representation of the dust composition, as well as for remote sensing of dust absorption in the UV\u2013vis spectral region

Silicon and chromium stable isotopic systematics during basalt weathering and lateritisation: A comparison of variably weathered basalt profiles in the Deccan Traps, India

Global biomass production is fundamentally affected by the hydrological cycling of elements at the Earth's surface. Continental weathering processes are the major source for most bio-essential elements in marine environments and therefore affect primary productivity. In addition, critical zone biomass depends on energy and chemical exchange reactions in weathering profiles. The latter reservoirs are in turn influenced by different climatic conditions that control weathering and pore water parameters like pH and Eh, which regulate mineral break down rates and dictate the mobility and mass flux of elements. Two Deccan Traps basalt weathering profiles of contrasting age and alteration intensity provide a natural laboratory for investigating the effects of rock alteration on Si and Cr and their isotopic. systematics. The Quaternary Chhindwara profile has progressed to a moderate degree of alteration (saprolite), while the Paleogene Bidar example displays an extremely altered laterite. The Chhindwara saprolite profile shows a near uniform Cr and Si concentration and isotopic composition, whereas the Bidar laterite profile is characterised by an intense loss of Si, a large enrichment of Cr within the most altered uppermost levels, and a wide range of Cr stable isotope ratios (-0.85 to 0.36 parts per thousand delta Cr-53/52). A co-variation between Si and Cr isotopes, as well as their co-variation with iron content, provides empirical evidence that iron redistribution within the profile has a large effect on Cr mobility and Si isotopic fractionation. Therefore, it is concluded that iron oxides exert a primary control over the isotopic composition of both Cr and Si in pore waters of laterites. Since laterite formation is promoted by tropical climates, the results of this study provide new evidence to suggest that the hydrological Cr and Si fluxes originating from continental weathering have changed in accordance with large-scale, deep time climate variation and continental plate configuration. An increased flux of Si and greater magnitude of Cr mobility and isotopic fractionation are possibly amplified under CO2-rich, greenhouse episodes and/or when large landmasses were tectonically arranged at near equatorial latitudes

MedAustron Beam Vacuum System: From Sources to Patient Treatment Rooms

The MedAustron beam vacuum system is a complex system integrating different technical solutions from the source to the patient treatment rooms. The specified vacuum performances combined with the challenging integration issues require technical compromise which will be presented in this poster. The status of the design of the vacuum system will be reviewed and the pending issues will be explained

Coupling nickel chemical speciation and isotope ratios to decipher nickel dynamics in the Rinorea cf. bengalensis-soil system in Malaysian Borneo

Abstract: Aims. Rinorea cf. bengalensis is a Ni hyperaccumulator which occurs in Sabah (Malaysia), on Borneo Island, that is able to accumulate considerable amounts of Ni and influences the Ni cycle in surface soil layers, both in terms of Ni concentration and Ni isotopic composition. In this study, the biogeochemical processes underpinning Ni isotopic fractionation in the soil-plant system and the mechanisms regulating Ni homeostasis in R. cf. bengalensis plants were elucidated. Methods: Two specimens of R. cf. bengalensis of different ages and associated surface soils were collected from ultramafic soils in Sabah. Soil mineralogy, Ni concentrations, speciation and isotopic signatures were subsequently determined in plant and soil samples. Results: Nickel in R. cf. bengalensis leaves is mainly complexed with citrate. Soil Ni available fractions have different δNi values depending on the Ni bearing phases. Rinorea cf. bengalensis specimens take up lighter Ni isotopes and a pronounced isotopic fractionation within the plant is observed, especially in the young specimen. Conclusions: The results suggest that the observed fractionation in the young plant can be attributable to kinetic effects (lighter isotopes move faster), which become less evident in the older specimen, as Ni is redistributed and homogenized through phloem loading and unloading processes

Influence of trace level As or Ni on pyrite formation kinetics at low temperature

International audiencePyrite formation at low temperature during early diagenesis in (sub-)surface sediments is an essential step of Fe and S biogeochemical cycles and the presence of this ubiquitous mineral of surface environments is often used as an indicator of paleo-redox conditions. Pathways of pyrite formation are usually discussed in environmental settings by involving a variety of nanosized Fe-S mineralogical precursors as a function of the local geochemical conditions. However, the influence of trace element impurities such as Ni and As in the solution at the time of pyrite formation has been poorly studied, whereas specific chemical signatures of trace elements are commonly observed in sedimentary pyrites. A better understanding of the impact of Ni and As incorporation at trace levels on pyrite formation is essential to help refining the use of these elements as paleo-redox indicators and to evaluate the role of pyrite as a sink regulating the biogeochemical cycle of potentially toxic trace elements. In this study, we have performed syntheses of pyrite at low temperature by the polysulfide pathway using aqueous Fe(III) and H2S in the presence of trace amounts of Ni(II) (0.001 mol%Fe) and As(III) (0.001 mol%Fe). Analysis of the solids collected at different time steps over the course of the experiments using X-Ray absorption spectroscopy at both the Fe and S K-edges shows that pyrite starts to precipitate within 5 days in presence of Ni(II) and within 32 days in presence of As(III), while the control experiment showed an intermediate precipitation rate of 14 days. Shell-by-shell analysis of Fe K-edge EXAFS data shows that the initial mineralogical precursors are the same whatever the experimental conditions and correspond to poorly-crystalline FeS (3.0±0.1 [email protected] Å; 1.7±0.2 [email protected] Å). In addition, XANES qualitative analysis suggests the incorporation of small amounts of Fe(III) within these FeS precursors. Synchrotron-based XRD and WAXS-PDF analysis of the starting solids show that in addition to S(0), the FeS precursors correspond to a continuum of FeS particles that ranges from tetragonal nanocrystalline FeS (a = 3.70(2) Å, c = 5.24(7) Å, MCDab = 41±4 Å MCDc = 21±2 Å) to cluster-type FeS (MCDabc < 8.4±4.3 Å). We propose that Ni(II) and As(III) have a different type of interaction with these FeS precursors, resulting respectively in an increase and a decrease in the rate of pyrite nucleation. While Ni(II) would incorporate within the structure of the FeS precursors, As would interact with (poly)sulfides in solution to form thio-As, possibly binding or precipitating onto FeS surfaces and thus slowing FeS transformation to FeS2. Given that both Ni and As were introduced at trace levels in our experiments, these results suggest that the occurrence of trace amounts of impurities could have a strong influence on pyrite precipitation kinetics in natural settings such as pore-scale microenvironments. In addition to emphasizing the importance of trace elements such as Ni or As on the persistence of mobile colloidal FeS species in anoxic conditions, the results of the present study also point to the importance of considering the actual nature of the impurities when using pyrite composition for ancient environments and past climates reconstruction

Coupling nickel chemical speciation and isotope ratios to decipher nickel dynamics in the Rinorea cf. bengalensis-soil system in Malaysian Borneo

Abstract: Aims. Rinorea cf. bengalensis is a Ni hyperaccumulator which occurs in Sabah (Malaysia), on Borneo Island, that is able to accumulate considerable amounts of Ni and influences the Ni cycle in surface soil layers, both in terms of Ni concentration and Ni isotopic composition. In this study, the biogeochemical processes underpinning Ni isotopic fractionation in the soil-plant system and the mechanisms regulating Ni homeostasis in R. cf. bengalensis plants were elucidated. Methods: Two specimens of R. cf. bengalensis of different ages and associated surface soils were collected from ultramafic soils in Sabah. Soil mineralogy, Ni concentrations, speciation and isotopic signatures were subsequently determined in plant and soil samples. Results: Nickel in R. cf. bengalensis leaves is mainly complexed with citrate. Soil Ni available fractions have different δ60Ni values depending on the Ni bearing phases. Rinorea cf. bengalensis specimens take up lighter Ni isotopes and a pronounced isotopic fractionation within the plant is observed, especially in the young specimen. Conclusions: The results suggest that the observed fractionation in the young plant can be attributable to kinetic effects (lighter isotopes move faster), which become less evident in the older specimen, as Ni is redistributed and homogenized through phloem loading and unloading processes

Strontium isotope tracing of terrigenous sediment dispersal in the Antarctic Circumpolar Current: Implications for constraining frontal positions

International audienceThe vigor of the glacial Antarctic Circumpolar Current (ACC) and the locations of frontal boundaries are important parameters for understanding the role of the Southern Ocean in global climate change. Toward the goal of understanding the locations of currents we present a survey of Sr isotope ratios in terrigenous sediments around the perimeter of Antarctica. The pattern of the variations within the modern ACC is used to suggest that terrigenous sediment from Antarctica is injected into the ACC via the Ross and Weddell gyres in the south. North of the main ACC the Sr isotopes reflect continental contributions from Africa, Australia-New Zealand, and South America. Along a transect northward from the Ross Sea, Sr isotope ratios show a decrease from higher values in the south (Antarctic provenance) to lower values in the north (provenance from New Zealand). This otherwise monotonic decrease is interrupted within the ACC by a ''zigzag'' to lower and then higher values, which accompanies minimum terrigenous flux. This zigzag requires contributions from two additional sediment sources beyond the main Antarctic and New Zealand end-members. The lower Sr isotope ratios are attributable to greater contributions from basaltic sources within the current, a consistent pattern around the ACC. The samples with higher Sr isotope ratios point to an additional contributor, possibly a wind-transported component from Australia. During the LGM there is a systematic geographical variation in the Sr isotope ratios, similar to that of the Holocene. A small offset of the zigzag to the north (approximately 1°–2°) may indicate a small northward shift of the southern boundary of the ACC. More highly resolved data are required to test whether this northward shift is really significant and whether it applies to other ACC fronts during the LGM

Quantification of rapid environmental redox processes with quick-scanning x-ray absorption spectroscopy (Q-XAS)

Quantification of the initial rates of environmental reactions at the mineral/water interface is a fundamental prerequisite to determining reaction mechanisms and contaminant transport modeling and predicting environmental risk. Until recently, experimental techniques with adequate time resolution and elemental sensitivity to measure initial rates of the wide variety of environmental reactions were quite limited. Techniques such as electron paramagnetic resonance and Fourier transform infrared spectroscopies suffer from limited elemental specificity and poor sensitivity to inorganic elements, respectively. Ex situ analysis of batch and stirred-flow systems provides high elemental sensitivity; however, their time resolution is inadequate to characterize rapid environmental reactions. Here we apply quick-scanning x-ray absorption spectroscopy (Q-XAS), at sub-second time-scales, to measure the initial oxidation rate of As(III) to As(V) by hydrous manganese(IV) oxide. Using Q-XAS, As(III) and As(V) concentrations were determined every 0.98 s in batch reactions. The initial apparent As(III) depletion rate constants (t < 30 s) measured with Q-XAS are nearly twice as large as rate constants measured with traditional analytical techniques. Our results demonstrate the importance of developing analytical techniques capable of analyzing environmental reactions on the same time scale as they occur. Given the high sensitivity, elemental specificity, and time resolution of Q-XAS, it has many potential applications. They could include measuring not only redox reactions but also dissolution/precipitation reactions, such as the formation and/or reductive dissolution of Fe(III) (hydr)oxides, solid-phase transformations (i.e., formation of layered-double hydroxide minerals), or almost any other reaction occurring in aqueous media that can be measured using x-ray absorption spectroscopy